(a) Field of the Invention
The present invention relates to a gear shifting method of a hybrid vehicle that combines an engine and a motor to generate a rotation torque and to transfer the rotation torque to an output shaft through a transmission.
(b) Description of the Related Art
Generally, an automatic transmission uses a hydraulic pressure to shift gears in a multi step process so as to output appropriate torque from the rotation torque of an engine/motor according to a driving condition. Some hybrid vehicles use two motor/generators (MG) and one engine that are connected through a planetary gear and control the motor/generator to achieve a continuous variable shifting.
Typically, at least two motors and one planetary gear set are used in combination to create an electric continuously variable transmission (CVT) so that the speed of the engine can be freely controlled thereby. Clutches and/or brakes are often used between the planetary gear sets or the rotational elements thereof. By releasing and/or engaging the clutches and/or the brakes in the CVT transmission, rotational characteristics of the motors and the engine may be controlled. In a conventional CVT, the clutches and/or the brakes are released so as to prevent the torque from being transferred to the transmission output in a Neutral (N) mode or a Park (P) mode of the transmission.
When the transmission is transferred from a park or neutral condition to a drive (D) or reverse (R) position, slippage occurs in the clutch and the brake due to a rotational speed difference. As a result, vibration/noise is formed by the frictional force and the durability of the transmission is decreased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.